Method and a system for distribution of fluidisable materials

ABSTRACT

The present invention relates to a method and a system for distribution of fluidisable materials from a reservoir ( 1 ) of materials to one or more material receiving units. In accordance with the invention the distribution system has at least two hydraulic levels between the reservoir and the material receiving units. The system further includes a novel fluidising element with good dynamic response properties. The system may preferably be used for distribution of alumina and/or fluoride to feeding equipment in electrolysis cells with a reduced consume of fluidising gas.

[0001] The present invention relates to a method and a system for distribution of fluidisable materials. In particular the invention relates to distribution of fluidisable materials such as fluoride and/or aluminium oxide (alumina) within an electrolysis facility for the production of aluminium.

[0002] NO patent 175876 describes an apparatus for transport of powder materials by fluidising the materials. The apparatus comprises an enclosed first fluidised channel for distribution of materials from a reservoir to a plurality of outlets. At each outlet there are arranged feeding devices for individual feeding of materials such as alumina to separate feeding holes in the crust of an electrolysis cell. The channel for distribution of materials comprises two horizontally divided sections where the sections are divided by means of a porous wall. The upper section is completely filled with fluidised materials, while the lower section act as a distribution chamber for fluidising gas. The lower section is provided with fluidising gas by means of a fan. The mentioned feeding devices comprises at least one second fluidised channel having plural outlets shaped as downwardly directed tubes. The outlets are surrounded by a casing having feeding holes in its bottom. The downwardly directed tubes end above the bottom part of the casing, and material leaving the outlets will be blocked as the level of material in the casing reaches a certain level. As materials are consumed, the level in the casing will drop and said outlets will be free of materials. Followingly, materials will start to flow into the casing from the reservoir through the first fluidising channel and into the feeding device via the second fluidising channel. To obtain this self-controlled feeding, the channels have to be fluidised continuously by the fan. Further, in said system the materials will be transported in accordance with one hydraulic step, and as a consequence of this the vertical level between the uppermost material storage and the lowermost material outlet becomes high. In an electrolysis facility such fluidised channels may have an extension of several hundred meters while the angular decline of the channel may be some degrees. Under certain unwanted circumstances such high static pressure differencies in the transport system may lead to an uncontrolled transportation of materials such as rapid drainage of materials from the storage with a resulting undesired over-feeding of materials to the electrolysis cell as a consequence. Further, the energy consume in the described system will be relatively high because the system is likely to be driven in a continuously fluidising modus to operate in a satisfying manner.

[0003] With the present invention the above mentioned disadvantages can be avoided. In accordance with the present invention the transport system have two or more hydraulic levels that are serially connected with each other by means of inlet locks. The system works with rapid material speeds while the fluidising channels will not be topped up by fluidised material. The fluidising gas supplied at each individual fluidising element will be discharged in a non-continuously (i.e. continuous in transport modus only), controlled manner thus keeping the energy consume at a minimum level. For this purpose there has been developed a fluidising element specially adapted to fit within the system. Further the non-continuously way of discharging fluidising gas will initiate a flushing of the system at each start-up thus draining the system for unwanted objects, large particles etc.

[0004] The invention shall further be described in the following by examples and figures where:

[0005]FIG. 1 shows the principles of transporting materials in accordance with the invention from a reservoir to a plurality of material receiving units,

[0006]FIG. 2 shows more details of the principles as defined in FIG. 1,

[0007]FIG. 3 discloses in part a cross-section view of a novel fluidising element for use in accordance with the invention,

[0008]FIG. 4 discloses an operating scheme for performing transport of fluidisable materials in accordance with the system.

[0009] In FIG. 1 there is shown a reservoir I comprising fluidisable powder materials 2. The reservoir is provided with a tubular outlet 3 at its bottom that protrudes into an inlet box 4. The feeding from the reservoir to the inlet box may be performed in accordance with the gravity feeding principle. The inlet box 4 is formed as a rectangular box and is provided with at least one fluidising element 5 at its bottom. In the figure the fluidising element is not shown in detail, but such elements are commonly placed along the bottom part of means containing materials to be fluidised. Preferably the element covers only a part of the bottom, and not the projected area with respect to the outlet 3. The fluidising element receives pressurised gas through an inlet pipe 6 that may have a controllable valve (not shown) for controlling the supply of pressurised gas to the element. Alternatively the fluidising elements of the system can be provided with inlet nozzles communicating with the inlet pipes where the nozzles are provided with an orifice size that gives a desired fluidising velocity through the fluidising elements. The inlet box 4 has further an outlet 8 that communicates with a pneumatic conveyer 9. The declination of this part of the conveyer is preferably about 3°. It should be understood that the term pneumatic conveyer in an embodiment may be similar to an air slide conveyer. The function of the inlet box is as follows: Powder material will be feeded from the reservoir towards the bottom of the inlet box 4. The geometrical design of the inlet box, the tubular outlet from the reservoir, together with the static or dynamic angle of slide of the material itself will cause an inclined built up of material towards the outlet 3 of the reservoir 1 (also indicated in FIG. 1). In periods of no transport of materials out of the inlet box, the transport of materials from the reservoir to the inlet box will stop completely. Preferably the length of the tubular outlet 3 is five times its inner diameter or more.

[0010] The pneumatic conveyer has preferably a plurality of fluidising elements 10, 11, 12, 13 arranged at its bottom part similar to that of element 5. Further, similar to that mentioned under element 5, these elements can receive pressurised gas through respective inlet pipes 14, 15, 16, 17 having controllable valves (not shown). In the conveyer, the part 9′ may advantageously be a separator for separating unwanted objects out of the conveyer. The separator is not shown in detail here, but can preferably be of a fluidisable type.

[0011] The sections of the conveyer such as section 9″ may have a declination of 1° with respect to the horizontal level. This small declination can be realized with the use of a novel fluidising element which will be further explained under FIG. 3. At its outlet end the section 9″ is connected with a distributor box 23 for the distribution of materials in at least two directions. The outlet 28 of said section comprises a downwards directed tube or pipe that ends above the bottom part of the distribution box. Preferably the length of the pipe is five times its inner diameter or more.

[0012] At its bottom part the distributor box 23 in this embodiment is provided with two fluidising elements 29, 29′ that covers partly its bottom. An inlet pipe 31, 31′ is connected with the fluidising element 29, 29′ via a controllable valve (not shown). Similar to that of the inlet box 4, the geometrical design of the distribution box, the arrangement of the tubular outlet from the reservoir, together with the static or dynamic angle of slide of the material itself will cause a inclining built up of material towards the outlet 28 of the section 9″ (also indicated in FIG. 1). The distributor box can in principle be provided with one or more fluidising elements, but in the present embodiment having two elements, these are preferably symmetrically arranged with respect to the outlet 28. The elements may be arranged with a space between them, thus not covering the projected area beneath the outlet 28.

[0013] The function of the distribution box is as follows: Powder material will be feeded from the outlet 28 of the conveyer section 9″ towards the bottom of the distributor box 23. In periods of no transport of materials out of the distributor box, the transport of materials from the conveyer section 9″ to the distributor box will stop completely. In this example there is shown a distributor box with two outlets 24, 25 connected with pneumatic conveyer sections 26, 27 respectively. However, it should be understood that the present principle of transporting fluidisable materials does not limit the distribution box to include only two outlets. The distributor box may for instance be circular seen from above and have the number of outlets required to suit in in each individual application.

[0014] In the Figure the conveyer sections 26 and 27 are identical, and therefore only the first mentioned section will be described in detail in the following. The declination of these conveyers is preferably about 10. As in the previously described conveyer sections, section 26 comprises one or more fluidising elements 36 arranged in its bottom and further connected with an inlet pipe 37 for pressurized gas that can be controlled by valve (not shown). It should be understood that in periods when at least one of these elements are activated, the fluidising element 29 is normally activated as well. As will be seen in the Figure, there is arranged two outlets 32, 33 in the partly shown conveyer section 26. These outlets communicates with intermediate storage tanks 34, 35 respectively, where material can be delivered for instance to individual electrolysis cells from each tank. Preferably the outlets 32, 33 are arranged as openings in one side wall of the conveyer that further are provided with downwards directed tubes. Sideways openings are preferred because if one tank 34 has been filled up and as a consequence the outlet 32 will be blocked by materials, the flow of materials through the section 26 will still be able to pass by the outlet without hindrance of materials that builds up in the outlet region.

[0015] In the bottom part of the tanks 34, 35 there are arranged tubular downwards directed outlets 39, 40 that feed materials to inlet boxes 41, 42 and conveyor sections 47, 51 respectively. Preferably, the length of the outlet tubes are five times their inner diameter or more. The boxes are individually identical and therefore only box 41 will be described here. Similar to the function of the inlet box 4, the inlet box 41 comprises at least one fluidisable element 43 provided with pressurised gas through pipe 44 controlled by a valve (not shown). Preferably the element covers only a part of the bottom, and not the projected area with respect to the outlet 39.

[0016] Powder material will be feeded from the outlet 39 towards the bottom of the inlet box 41. The geometrical design of the inlet box, the tubular outlet from the tank 34, together with the static or dynamic angle of slide of the material itself will cause a inclining built up of material towards the outlet 39 of the tank 34 (also indicated in FIG. 1). In periods of no transport of materials out of the inlet box, the transport of materials from the tank to the inlet box will stop completely.

[0017] The inlet box 41 has an outlet 46 that communicates with a pneumatic conveyer section 47 having one or more fluidising elements 48 connected with an inlet pipe 49 for pressurized gas that can be controlled by a valve (not shown). The declination of this conveyer is preferably about 1.5°. The conveyer section 47 may convey materials such as aluminium oxide and/or fluoride to the superstructure of an electrolysis cell (not shown) to appropriate feeding devices arranged therein (not shown). The declination of this part of the conveyer is preferably about 0.5°.

[0018]FIG. 2 discloses more details of the principles as described in FIG. 1. In FIG. 2 the same system as described in FIG. 1 is disclosed, but additional equipment such as de-aeration devices and different hydraulic levels are disclosed in this Figure. Advantageously there are arranged de-aeration pipes 100, 101, 102 between section 9 (see FIG. 1) and the reservoir 1, between section 9″ and section 9 or separator 9′, and finally between inlet box 41 and section 26 respectively. Preferably the elevation of the bends in this pipes is 250 millimetres or more above its upper connection point to avoid transport of materials through the de-aeration pipes.

[0019] In the Figure there is further marked different levels h0, h1, h2, h3 and h4. In a fluidised state the powder material will not act as particulate matter but will rather behave more like a fluid (liquid). In operation the various fluidising elements will normally not be activated at the same time. These elements will rather be operated either periodically or by demand in accordance with various transport patterns to ensure that materials are transported to all material receiving units in the system and that it delivers sufficient amount of materials within a predefined period of time. For instance there can be connected one or more feeding silos (arranged in the superstructure of each electrolysis cell) at the end of all conveyer sections similar to and including section 47 having a total capacity for some hours of operation. To deliver enough materials to fill this silos up, the branch of the conveying system comprising each section 47 just have to run part-time depending on powder velocity, storage capacity of feeding silos and cross section flow rate versus the actual consume. In periods where this branch is inactive, similar operations can be performed elsewhere in the system, thus saving momentary capacity of pressurized gas and energy.

[0020] In the Figure, level h1 at inlet box 41 indicates a liquid stop that will restrict fluidised materials above this level to pass through said level in a situation where materials have built up in the inlet box 41 and followingly blocks the outlet 39 of the tank 34. Similar situations will be representative for levels h2 and h3. At level h2, the distributor box 23 will act as a liquid stop, and followingly materials will be restricted from passing through this level as a result of material build up in this box. Accordingly, at level h3 the inlet box 4 will act as a liquid stop, restricting materials from leaving the reservoir 1. In the Figure, h1 indicates atmospheric pressure, while h0 indicates the feeding valve of the end user.

[0021] In operation, the system will be fluidised in branches. For instance. in one period one branch including inlet box 4, conveyer 9 and 9″, distributor box 23, and at least a part of conveyer section 26 will be activated by fluidising gas and materials will flow from the reservoir 1 and to the tank 34. As tank 34 has been filled up, the part of the conveyer 26 between tank 34 and tank 35 can be fluidised to cause transport of materials to tank 35. If materials still are required downstream the conveyer section 26, materials will continue to flow and pass by the inlet 32 of the tank 34, and the inlet 33 of the tank 35. At the end when all receivers downstream conveyer section 26 have become filled up the flow of materials in section 26 will be braked to rest. Assuming that there is no flow of materials in conveyer section 27, then there will be a material build-up in the distributor box 23 and followingly the material flow through conveyer sections 9″ and 9 will be braked and brought to rest. Following that, the inlet box 4 will receive a build up of material and flow of materials from reservoir 1 to inlet box will be stopped.

[0022] If material fill-up is required dowstream tank 34 for instance with respect to the conveyor section 47, this can be performed by activating the fluidising elements 48 in section 47. Materials will then start to flow from tank 34 towards the material receiving unit(s). At the end when no more materials is required downstream said conveyer section 47, the material flow will be braked in branch 47 and the inlet box 41 will be blocked by material build-up.

[0023] If then the similar conveyer section 27 (see also FIG. 1) is activated by running fluidising gas through the fluidising elements therein, materials will start to flow through section 27 into similar tanks as previously described tanks 34 and 35, and in accordance with a similar procedure. The material build up in the distributor box 23 will then cease to exist because materials is removed from that location downwards conveyer 27. The fluid stop is then inactive, and followingly materials will start to flow into the distributor box 23 from conveyer 9″ and 9. The fluid stop at inlet box 4 will then be inactive of same reason as mentioned under the distributor box, and followingly materials will start to flow from reservoir 1 through the inlet box 4. This flow will continue as long as the fluidising elements involved are active and until the similar tanks are filled up. At the end the flow of fluidized materials will cease and stop in accordance with the pattern as described under the first mentioned branch including conveyer section 26.

[0024] It should be understood that the material transport performed by the distribution system may be controlled by a computer processing unit (not shown). Accordingly, there may be indicating means such as material level sensing means (not shown) in various elements of the distribution system. These sensing means may be connected with the processing unit which further may activate/deactivate the various fluidising elements throughout the system in accordance with a defined program.

[0025] In FIG. 3 there is shown in part a cross-section cut through a conveyer channel 200 having a bottom 201, side parts 202, 203. In the upper part of the figure there is shown a wave-shaped line indicating that the channel continues above the level of said line. The fluidising element comprises an inlet 205, base plate 204 and a gas permeable element 206. The element can be made out of a web-material and is fixed at its peripheral parts to the base plate 204. In the figure, the web material is fixed by bending the outer side parts of the base plate to clamp the peripheral side parts of the web material. The base plate can be made out of a metal material, such as a steel plate. To avoid leakage of fluidising gas, the connection between the web material and the base plate may be provided with a gasket element 208, 209. The gasket element may be of any appropriate gasket material able to withstand the physical and chemical environment in the conveyer. The above mentioned way of fixing the parts together applies similarly to the end sides of both the base plate and the web material.

[0026] The inlet 205 is constituted by a pipeline fitting 210 comprising a vertical extending pipe 211 with an orifice 212. An protective element 213 is arranged between the gas permeable element 206 and the orifice 212 to protect the element against perforation. The element may be provided with openings in one or more of its side surfaces, or be open ended as indicated in the figure. The base plate 204 of the fluidising element is provided with an internally threaded part 215 communicating with a hollow, sleeved nut 214 having external threads. This arrangement passes through a hole in the bottom 201 of the conveyer channel, thus serving to keep the fluidising element fixed to the bottom of the conveyer channel. Projections 216, 217 may be arranged in the side parts 202, 203 of the channel to secure the fluidising element against unwanted displacements.

[0027] One special advantage related to the fluidising element as described above is that the plenum-chember has a very little volume, thus rendering a quick fluidising response of the material when fluidising gas is introduced into the plenum-chamber. This further implies that unwanted non-fluidisable objects in the transport system can be gradually moved out of the system by the relatively strong gas-flow pulse that occurs by the activation of the element. Preferably the fluidising velocity through the permeable part of the fluidising elements is set to 0.02 meters per second (i.e. volume of fluidising gas per second versus the area of the permeable part of the fluidising element).

[0028]FIG. 4 discloses an operating scheme for performing transport of fluidisable materials in accordance with the system. In the scheme there are similar components as those described in FIG. 1, where a reservoir 301 communicates with a inlet box 304. The inlet box communicates with a conveyer 309 having at least one fluidising element F. The conveyer is connected with a distribution box 323 that can distributes material in conveyer 326 and/or conveyer 327. Conveyer 326 transports materials to six tanks 334-339, while conveyer 327 transports materials a similar number of tanks. The systems concerned with conveyer 326 and the conveyer 327 are in this embodiment identical (not all parts shown) and thus only one conveyer will be described here. Downstream the distributor 323 there is arranged one fluidising element f1. When activating element F in conveyer 309 and said element, materials will be transported from reservoir 301 to tank 334 with little consume of pressurised gas. Controlled by time and possibly by full-tank indication, the fluidising element f2 will be activated while F and f1 still are active. Then tank 335 may be filled up by the material transport. Controlled in the same manner as that for the previous tank, fluidising element f will be activated, thus initiating filling of tank 336. Similar procedures can be carried out for tanks 337, 338, and 339. Then a similar procedure can be carried out to fill similar tanks connected with conveyer 327, where the fluidising elements f7-f12 can be activated successively. The average consume of pressurised gas can be calculated on the basis of the following relation based upon the average activation time of the fluidising elements: F+(f1 . . . fn)×½. the suffix “n” indicates the total number of fluidising elements and correspondingly the number of tanks in one conveyer similar to the conveyer 326.

[0029] In the above mentioned embodiment the fluidising elements are fluidised progressively one by one to fill the tanks one by one. Alternatively, groups of tanks can be filled in one sequence. For instance the fluidising elements f1 and f2 can be activated simultaneously, to fill tank 334 and 335 in one sequence. As tank 335 has been filled up, for instance sensed by a level indicator (not shown), the elements f3 and f4 can be activated to carry out similar filling procedure.

[0030] In the figure there is schematically shown an electrolysis cell E feeded by materials from feeding units 350-355. Such feeders may commonly be constituted by a small reservoir and a metering device for feeding materials into the cell through a pipe 360 or the like. The feeders receive materials from a conveyer 347 fluidised by one or more fluidising elements F3. As the element F3 is activated, materials will start to flow from tank 336 through inlet box 341 and into the conveyer 347. The feeding units 350-355 will then receive material and become filled up. Preferably this latter branch is not activated when filling of tank 336 is carried out, to avoid possible direct flow of materials from reservoir 301 and to the feeding units 350-355. However, there will be defined hydraulic levels with restrictions/blocks between them even though the system is fluidised in conveyers from start to end that will make such direct flow possible. This is because the projected area of the downwards directed inlets in the inlet boxes, together with the length versus diameter relation of said inlets will initiate non-fluidised flow restrictions in the system.

[0031] Preferably, the transport of materials in the system is carried out in the most economical manner with respect to instant pressurised gas capacity, and to satisfy the requirements with regard to all-over minimum filling levels.

[0032] It should be understood that the control of the feeding units 350-355 preferably is connected with the operation of the electrolysis cell, and the discharge out of this units can be controlled in accordance with a cell control programme not further specified here.

[0033] The system as described above will sustain several advantages. One important feature is that the relatively small, batchwise transportation and distribution to a plurality of material receivers will contribute to counteract segregation and thus to homogenize the material. Thus the consequences of variations in the quality of the material to be distributed will be evened out between all material receivers in the system. 

1. A method for distribution of fluidisable materials comprising a reservoir (1) for the material to be distributed, fluidisable conveying means (9, 26, 27, 47) distributing the material to one or more material receiving units (34, 35), characterised in that the material is distributed from the reservoir to the material receiving units through at least two hydraulic levels defined by one or more inlet locks (4, 23, 41)
 2. A method in accordance with claim 1, characterised in that the fluidisable conveying means (9, 26, 27, 47) are activated by pressurised fluidising gas in a non-continuous manner.
 3. A method in accordance with claim 1, characterised in that the fluidisable material is distributed to one or more electrolysis cells (E) for the production of aluminium.
 4. A method in accordance with claim 1, characterised in that the fluidisable conveying means (9, 26, 27,) is activated and controlled by means of a pre-programmed computer in a manner where the fluidising elements are activated in a progressive manner.
 5. A system for distribution of fluidisable materials comprising a reservoir (1) for the material to be distributed, fluidisable conveying means (9, 26, 27, 47) for the distribution of the materials to one or more material receiving units (350), characterised in that the conveying means (9, 26, 27, 47) comprises at least one material lock (4, 23, 41) thus defining at least two hydraulic levels in the conveying means.
 6. A system in accordance with claim 5, characterised in that the fluidisable conveying means (9, 26, 27, 47) comprises a plurality of branches for the distribution of fluidisable materials to a plurality of material receiving units (350-355) thus defining a plurality of distribution paths between the reservoir (1) and each individual material receiving units where each path is fluidised by pressurised gas in a non-continuous manner.
 7. A system in accordance with claim 5, characterised in that the material lock (4, 23, 41) comprises a downwardly directed inlet (3, 28, 39), a partly fluidisable bottom and an outlet (8, 24, 46) communicating with a fluidisable conveyer (9, 26, 47).
 8. A system in accordance with claim 5, characterised in that the fluidisable conveying means (9, 26, 27, 47) comprises at least one fluidising element constituted by a base plate (204), an inlet (205) for pressurised gas and a gas permeable element (206) attached to said base plate thus forming a plenum chamber between the base plate and the gas permeable element.
 9. A system in accordance with claim 5, characterised in that the fluidisable material is alumina or fluoride distributed to one or more electrolysis cells.
 10. A system in accordance with claim 5, characterised in that the material receiving units (350) are one or more feeding devices arranged in electrolysis cells (E). 